Along with the rapid development of a wireless multimedia service, since there is an increasingly demand of people for high data rate and user experience, a higher requirement for system capacity and coverage of the conventional Long Term Evolution (LTE) is pushed forward. In the conventional LTE cellular network, a macro eNB provides an access service for User Equipment (UE) as a unique network element at an access side. In order to meet the demand of the user on the higher data rate and improve the spectral efficiency of the cellular network, a great number of Low Power Nodes (LPNs) are deployed by the operator in the LTE cellular network to take as a supplement of the macro eNB and provide the access service for the UE. The LPN has the characteristics of low cost, low power, convenience in deployment and the like and generally may include two deployment scenarios, namely hotspot deployment and enhanced coverage. Through the LPN, the data rate of a high-rate data service in an indoor or outdoor hotspot area can be effectively improved and the edge coverage in a remote area or cell is improved. Usually, the LPN also can be called as a small eNB and may include but not limited to: a Home eNB (HeNB), a pico eNB, a Remote Radio Unit/Head (RRU/RRH) and a Relay Node (RN). However, due to a fact that the coverage range of a small cell under the small eNB is relatively small, the probability of handover failure when a medium-high speed mobile UE passes through the small eNB is increased and thus the service continuity of the UE is affected. To improve the mobility performance of the UE after being introduced to the small cell, there pushes forward in the industry that the basic coverage is guaranteed by a certain eNB (for example: the macro eNB), the UE always keeps a Radio Recourse Control (RRC) connection with the eNB and the small cell is only taken as a Transmission Point (TP) so as to provide the high data rate and meet the power-saving requirement of the user. FIG. 1 is a schematic diagram of a dual connectivity architecture according to a related art. As shown in FIG. 1, under such architecture, the UE at least keeps the connection with two eNBs and uses wireless resources under two eNBs, such that the cross-node wireless resource aggregation may be implemented. The architecture here is often called as the dual connectivity architecture. One having certain management control ability in the two eNBs connected with the UE is generally called as a Master eNB (MeNB) and the other is called as a Secondary eNB (SeNB).
For each UE, on a control plane, the MeNB may be connected to a Mobility Management Entity (MME) by an S1-MME and may be connected to the SeNB by an X2-C. On a user plane, for a Master Clock Generator (MCG) bearer, the MeNB may be connected to a Serving Gateway (S-GW) by an S1-U, whereas the SeNB does not participate in data transmission on the user plane. For a split bearer, the MeNB may be connected to the S-GW by the S1-U, whereas the MeNB may be connected to the SeNB by the X2-U. For a SCG bearer, the SeNB may be connected to the S-GW by the S1-U, whereas the MeNB does not participate in the data transmission on the user plane.
FIG. 2 is a schematic diagram of a data protocol stack for an LTE user plane according to a related art. As shown in FIG. 2, downlink data received from a core network via a General Packet Radio Service (GPRS) Tunneling Protocol for the User Plane (GTP-U) are unpacked and then are processed through a Packet Data Convergence Protocol (PDCP) sublayer, a Radio Link Control (RLC) protocol sublayer, a Medium Access Control (MAC) protocol sublayer and a Physical Layer (PHY), and are finally transmitted to the UE. The transmission of the uplink data is the other way around with that of the downlink data. When the dual connectivity in Release 12 is discussed in a 3rd Generation Partnership Project (3GPP), two shunting manners for the user plane were mentioned.
Shunting manner 1: FIG. 3 is a schematic diagram of a shunting manner for a 1A user plane according to the related art. As shown in FIG. 3, bearer user planes of the UE on the MeNB and the SeNB are directly connected to the S-GW.
Shunting manner 2: FIG. 4 is a schematic diagram of a shunting manner for a 3C user plane according to the related art. As shown in FIG. 4, the MeNB may be taken as a shunting anchor point, and data are shunted at the PDCP and RLC layers and are respectively transmitted to the MeNB and the SeNB to be further transferred.
When the dual connectivity in the Release 12 is discussed in the 3GPP, a scenario of changing the SeNB is mentioned, that is, the UE is in dual connectivity with the MeNB and a Source SeNB (S-SeNB) before the handover and is in connection with the MeNB and a Target SeNB (T-SeNB) after the handover. Moreover, a scenario of changing the MeNB to the eNB is also mentioned, that is, the UE is in dual connectivity with the Source MeNB (S-MeNB) and the S-SeNB before the handover and is in single connection with the T-eNB after the handover. At present, when the dual connectivity enhancement in Release 13 is discussed in the 3GPP, a scenario of a handover between MeNBs (inter-MeNB handover) with the SeNB unchanged are being mentioned, that is, the UE is in dual connectivity with the S-MeNB and the SeNB before the handover and is in dual connectivity with the T-MeNB and the SeNB after the handover. A scenario of adding the SeNB after the handover are being mentioned, that is, the UE is in single connection with the eNB before the handover and is in dual connectivity with the T-SeNB and the T-MeNB after handover. Additionally, inter-MeNB handover together with the inter-SeNB handover is also being discussed, that is, the UE is in dual connectivity with the S-MeNB and the S-SeNB before the handover and is in dual connectivity with the T-MeNB and T-SeNB after the handover.
FIG. 5 is a signaling flowchart showing a process of an inter-MeNB handover with an SeNB unchanged according to the related art. As shown in FIG. 5, the signaling flowchart may include the following steps.
In step 1, the S-MeNB sends a handover request to the T-MeNB.
In step 2, the T-MeNB responds to the handover request and sends an SeNB modification request to the SeNB.
In step 3, the SeNB returns an SeNB modification request confirmation to the T-MeNB.
In step 4, the T-MeNB returns a handover request confirmation to the S-MeNB.
In step 5, the S-MeNB sends an SeNB release request to the SeNB.
In step 6, the S-MeNB sends an RRC connection reconfiguration to the UE.
In step 7, the UE enters a random access process with the T-MeNB.
In step 8, the UE sends an RRC connection reconfiguration completion to the T-MeNB.
In step 9, the UE enter a random access process with the SeNB.
In step 10, the T-MeNB sends an SeNB reconfiguration completion to the SeNB.
In step 11, the S-MeNB sends SN state transmission to the T-MeNB.
In step 12, Data forwarding is performed between the S-GW and the S-MeNB as well as between the S-MeNB and the T-MeNB.
In step 13, the T-MeNB sends a path conversion request to the MME.
In step 14, bearer modification is performed between the S-GW and the MME.
In step 15a, a new path is established between the S-GW and the T-MeNB.
In step 15b, a new path for the SCG bearer is established between the S-GW and the SeNB.
In step 16, the MME returns a path conversion request confirmation to the T-MeNB.
In step 17, the T-MeNB sends UE context release to the S-MeNB.
In step 18, the S-MeNB sends the UE context release to the SeNB.
During inter-MeNB handover with the SeNB unchanged, the data forwarding of the MCG bearer is performed from the S-MeNB to the T-MeNB (i.e., S-MeNB→T-MeNB). In the SCG bearer, for adding or modifying bearer, the data forwarding is at first performed from the SeNB to the S-MeNB, then is performed from the S-MeNB to the T-MeNB and finally is performed from the T-MeNB to the SeNB in sequence (i.e., SeNB→S-MeNB→T-MeNB→SeNB), and for deleting bearer, the data forwarding is at first performed from the SeNB to the S-MeNB and then is performed from the S-MeNB to the T-MeNB in sequence (i.e., SeNB→S-MeNB→T-MeNB). In the split bearer, for adding or modifying bearer, the data forwarding is at first performed from the SeNB to the S-MeNB and then is performed from the S-MeNB to the T-MeNB in sequence (i.e., SeNB→S-MeNB→T-MeNB), and thereafter the data are transmitted from the T-MeNB to the SeNB; and for deleting bearer, the data forwarding is at first performed from the SeNB to the S-MeNB and then is performed from the S-MeNB to the T-MeNB in sequence (i.e., SeNB→S-MeNB→T-MeNB). Considering that the bearer type is changed during inter-MeNB handover with the SeNB unchanged, when the bearer type is changed from the SCG into the MCG, the data forwarding is at at first performed from the SeNB to the MeNB and then is performed from the S-MeNB to the T-MeNB in sequence (i.e., SeNB→S-MeNB→T-MeNB). When the bearer type is changed from the MCG into the SCG, the data forwarding is first preformed from the S-MeNB to the T-MeNB and then is performed from the T-MeNB to the SeNB in sequence (i.e., S-MeNB→T-MeNB→eNB). When the bearer type is changed from the split bearer into the MCG bearer, the data forwarding is first performed from the SeNB to the S-MeNB and then is performed from the S-MeNB to the T-MeNB (i.e., SeNB→S-MeNB→T-MeNB). When the bearer type is changed from the MCG bearer into the split bearer, the data forwarding is at first performed from the S-MeNB to the T-MeNB (i.e., S-MeNB→T-MeNB), and thereafter the data are transmitted to the SeNB from the T-MeNB.
During inter-MeNB handover with the SeNB unchanged, in the SCG bearer, for deleting hearer, the data forwarding can be optimized to be performed from SeNB to the T-MeNB (i.e., SeNB→T-MeNB). When the bearer type is changed from the SCG into the MCG during inter-MeNB handover with the SeNB unchanged, the data forwarding may be optimized to be performed from the SeNB to the T-MeNB (i.e., SeNB→T-MeNB). In addition, when the bearer type is changed from the MCG into the SCG during inter-MeNB handover with the SeNB unchanged, the data forwarding may be optimized to be performed from the S-MeNB to the SeNB (i.e., S-MeNB→SeNB).
FIG. 6 is a signaling flowchart showing that an SeNB is added after handover according to the related art. As shown in FIG. 6, the signaling flowchart may include the following steps.
In step 1, the eNB sends a handover request to the T-MeNB.
In step 2, the T-MeNB responds to the handover request and sends an SeNB adding request to the T-SeNB.
In step 3, the T-SeNB returns an SeNB adding request confirmation to the T-MeNB.
In step 4, the T-MeNB returns a handover request confirmation to the eNB.
In step 5, the eNB sends an RRC connection reconfiguration to the UE.
In step 6, the UE enters a random access process with the T-MeNB.
In step 7, the UE sends an RRC connection reconfiguration completion to the T-MeNB.
In step 8, the UE enter a random access process with the T-SeNB.
In step 9, the T-MeNB sends an SeNB reconfiguration completion to the T-SeNB.
In step 10, the eNB sends SN state transmission to the T-MeNB.
In step 11, data forwarding is performed between the S-GW and the eNB as well as between the eNB and the T-MeNB.
In step 12, the T-MeNB sends a path conversion request to the MME.
In step 13, bearer modification is performed between the S-GW and the MME.
In step 14a, a new path is established between the S-GW and the T-MeNB.
In step 14b, a new path for the SCG bearer is established between the S-GW and the T-SeNB.
In step 15, the MME returns a path conversion request confirmation to the T-MeNB.
In step 16, the T-MeNB sends UE context release to the eNB.
In the process of adding the SeNB after the handover, the data forwarding of the MCG bearer is performed from the eNB to the T-MeNB (i.e., eNB→T-MeNB). The data forwarding of the SCG bearer is at first performed from the eNB to the T-MeNB and then performed from the T-MeNB to the T-SeNB (i.e., eNB-→T-MeNB→T-SeNB). The data forwarding of the split bearer is at first performed from the eNB to the T-MeNB and thereafter the data are transmitted from the T-MeNB to the T-SeNB. Considering that the bearer type is changed in the process of adding the SeNB after the handover, when the bearer type is changed from the MCG bearer into the SCG bearer, the data forwarding is at first performed from the eNB to the T-MeNB and then performed from the T-MeNB to the T-SeNB in sequence (i.e., eNB→T-MeNB→T-SeNB). When the bearer type is changed from the MCG bearer into the split bearer, the data forwarding is at first performed from the eNB to the T-MeNB (i.e., eNB→T-MeNB) and thereafter the data are transmitted from the T-MeNB to the T-SeNB.
In the process of adding the SeNB after the handover, for the SCG bearer, the data forwarding may be optimized to be performed from the eNB to the T-SeNB (i.e., eNB→T-SeNB). In the process of adding the SeNB after the handover, when the bearer type is changed from the MCG bearer into the SCG bearer, the data forwarding may be optimized to be performed from the eNB to the T-SeNB (i.e., eNB→T-SeNB).
FIG. 7 is a signaling flowchart showing a process during the inter-MeNB inter-handover together with the SeNB handover according to the related art. As shown in FIG. 7, the signaling flowchart may include the following steps.
In step 1, the S-MeNB sends a handover request to the T-MeNB.
In step 2, the T-MeNB responds to the handover request and sends an SeNB adding request to the T-SeNB.
In step 3, the T-SeNB returns an SeNB adding request confirmation to the T-MeNB.
In step 4, the T-MeNB returns a handover request confirmation to the S-MeNB.
In step 5, the S-MeNB sends an RRC connection reconfiguration to the UE.
In step 6, the UE enters a random access process with the T-MeNB.
In step 7, the UE sends an RRC connection reconfiguration completion to the T-MeNB.
In step 8, the T-MeNB sends an SeNB reconfiguration completion to the T-SeNB.
In the step 9, the UE enter a random access process with the T-SeNB.
In step 10, the S-MeNB sends an SeNB release request to the S-SeNB.
In step 11a, the S-SeNB sends SN state transmission to the S-MeNB.
In step 11b, the S-MeNB sends SN state transmission to the T-MeNB.
In step 11c, the T-MeNB sends SN state transmission to the T-SeNB.
In step 12, data forwarding is performed between the S-GW and the S-SeNB, between the S-SeNB and the S-MeNB, between the S-MeNB and the T-MeNB, as well as between the T-MeNB and the T-SeNB
In step 13, the T-MeNB sends a path conversion request to the MME.
In step 14, bearer modification is performed between the S-GW and the MME.
In step 15, the marking and the grouping are finished.
In step 16, a new path is established between the S-GW and the T-MeNB.
In step 17, the MME returns a path conversion request confirmation to the T-MeNB.
In step 18, the T-MeNB sends UE context release to the S-MeNB.
In step 19, the S-MeNB sends UE context release to the S-SeNB.
During inter-MeNB handover together with inter-SeNB handover, the data forwarding of the MCG bearer is performed from the S-MeNB to the T-MeNB (i.e., S-MeNB→T-MeNB). The data forwarding of the SCG bearer is at first performed from the S-SeNB to the S-MeNB, then is performed from the S-MeNB to the T-MeNB and then is performed from the T-MeNB to the T-SeNB in sequence S-SeNB→S-MeNB→T-MeNB→T-SeNB). The data forwarding of the split bearer is at first performed from the S-SeNB to the S-MeNB and then is performed from the S-MeNB to the T-MeNB (i.e., S-SeNB→S-MeNB→T-MeNB), and thereafter the data are transmitted from the T-MeNB to the T-SeNB. Considering that the bearer type is changed during inter-MeNB handover together with inter-SeNB handover, when the bearer type is changed from the MCG bearer into the SCG bearer, the data forwarding is at first performed from the S-MeNB to the T-MeNB and then performed from then performed from the T-MeNB to the T-SeNB in sequence (i.e., S-MeNB→T-MeNB→T-SeNB). When the bearer type is changed from the SCG bearer into the MCG bearer, data forwarding is at first performed from the S-SeNB to the S-MeNB and then performed from the S-MeNB to the T-MeNB in sequence (i.e., S-SeNB→S-MeNB→T-MeNB). When the bearer type is changed from the MCG bearer into the split bearer, data forwarding is at first performed from the S-MeNB to the T-MeNB (i.e., S-MeNB→T-MeNB) and thereafter the data are transmitted from the T-MeNB to the T-SeNB. When the bearer type is changed from the split bearer into the MCG bearer, data forwarding is at first performed from the S-SeNB to the S-MeNB and then performed from the S-MeNB to the T-MeNB (i.e., S-SeNB→S-MeNB→T-MeNB), and thereafter the data are transmitted from the T-MeNB to the T-SeNB.
During inter-MeNB handover together with inter-SeNB handover, for the SCG bearer, the data forwarding may be optimized to be performed from the S-SeNB to the T-SeNB (i.e., S-SeNB→T-SeNB), or the data forwarding may be optimized to be at first performed from the S-SeNB to the S-MeNB and then performed from the S-MeNB to the T-SeNB (i.e., S-SeNB→S-MeNB→T-SeNB), or the data forwarding may be optimized to be at first performed from the S-SeNB to the T-MeNB and then performed from the T-MeNB to the T-SeNB (i.e., S-SeNB→T-MeNB→T-SeNB). During inter-MeNB handover together with inter-SeNB handover, when the bearer type is changed from the MCG bearer into the SCG bearer, the data forwarding may be optimized to be performed from to be performed from the S-MeNB to the T-SeNB (i.e., S-MeNB→T-SeNB). When the bearer type is changed from the SCG bearer into the MCG bearer, the data forwarding may be optimized to be performed from the S-SeNB to the T-MeNB (i.e., S-SeNB→T-MeNB).